The growing interactiveness of home entertainment systems, particularly cable television, interactive television, and Internet set-top boxes, is placing greater demands on hand-operated controls.
Mice have been commonly used as user-manipulable GUI apparatus. Using a mouse, a user directs the movement of a cursor across a display screen by corresponding manual mouse movements.
Joystick-type devices have also been used. In particular, IBM Corporation's TrackPoint III pointing device (hereinafter "TrackPoint-type device" or "TrackPoint device") has been mounted in-keyboard in many laptop computers. A TrackPoint-type device includes a button-like structure resembling a pencil eraser and disposed between keys of a computer keyboard, has facilitated the use of graphical user interfaces (GUIs) in portable computers. The need for a mouse, and a flat working surface on which the user manipulates the mouse, is eliminated, because the user is able to manipulate the TrackPoint device entirely within the keyboard.
A conventional physical implementation of the TrackPoint III pointing device is described in co-pending, co-assigned U.S. patent application Ser. No. 08/181,648, filed Jan. 4, 1994. That implementation includes strain gauge sensors, and a post serving as a lever arm. By manipulating the post, the user flexes the strain gauges. Small analog signals produced by the strain gauges are interpreted by on-board software, and the cursor is moved accordingly.
The strain gauges produce a 1/2% full-scale signal change, and must be individually trimmed during manufacture to match their outputs. The manufacturing and trimming of the strain gauges, combined with the small analog signal they produce, contribute to the cost of the sensor, and of the electronics required to make a TrackPoint III system. Moreover, the small full-scale magnitude of the signal change places a burden on the data acquisition system which processes the strain gauge signals into cursor movement signals.
Therefore, an important objective in the design and manufacture of TrackPoint type devices is the reduction of these cost-adding factors.
These issues have been confronted in the design and manufacture of other types of user-manipulable electronic components. For instance, a conventional structure is taught in Hughes, U.S. Pat. No. 4,305,007, "Electronic Two Directional Control Apparatus", issued Dec. 8, 1981. This patent describes a structure including four sensing electrodes, whose capacitances independently vary in response to the proximity of an external object.
A physical implementation of the Hughes structure is shown in FIG. 7 of the Hughes patent, which is reproduced as FIG. 1 of the present patent application. For simplicity, and to allow for a brief summary of the description of the Hughes structure, the reference numbers not directly pertinent to the summary have been deleted.
The Hughes structure includes sensing electrodes 5 that map out four quadrants. A controlling member 3 at the end of a displaceable member 2, supported from above by a ball joint 1, moves in relation to the sensing electrodes 5. These elements are contained within a three dimensional grounded shield box 4.
Note, however, that, in addition to being impractical for implementation in a keyboard or in a portable computer, the Hughes structure requires considerable cost for parts and assembly. Also, the manufacturing process must include manual trimming of the electronic circuit to match the outputs of the four quadrants. Therefore, the Hughes apparatus does not provide the desired low cost.